Electrophotographic drying and fixing device

ABSTRACT

An electrophotographic fixing device for a sheet which carries an electrophotographic image has a guide plate for guiding a copy sheet along a path. Electric heaters are located along the path for fixing the copy sheet, and in order to prevent contact of the copy sheet with the heaters, an elongated spacing wire is provided between the heaters and the copy sheet. The wire has a plurality of wire portions alternately bent in opposite directions toward and away from the path of the copy sheet, so that adjacent wire portions form kinks alternately projecting in opposite directions so that every second kink projects toward the copy sheet and forms a small engaging portion preventing scorching of the copy sheet when the copy sheet curls due to the heat.

United States Patent [191 Harwig et al.

[ ELECTROPIIOTOGRAPI-IIC DRYING AND FIXING DEVICE [75] Inventors: Karl Harwig, Unterhaching;

Juergen Vossnacke, Pullach, both of Germany [73] Assignee: AGFA-Gevaert Aktiengesellschaft,

Leverkusen, Germany 221 Filed: Jan. 26, 1973 21 Appl.No.:327,233

[30] Foreign Application Priority Data [58] Field of Search 432/59, 60, 62, 45, 227-232;

[56] References Cited UNITED STATES PATENTS 1,786,876 12/1930 Tessky 226/198 2,657,601 11/1953 Bentley 226/198 1 Sept. 17, 1974 Primary Examiner-John J. Camby Assistant Examiner-Henry C. Yuen Attorney, Agent, or Firm-Michael S. Striker ABSTRACT An electrophotographic fixing device for a sheet which carries an electrophotographic image has a guide plate for guiding a copy sheet along a path. Electric heaters are located along the path for fixing the copy sheet, and in order to prevent contact of the copy sheet with the heaters, an elongated spacing wire is provided between the heaters and the copy sheet. The wire has a plurality of wire portions alternately bent in opposite directions toward and away from the path of the copy sheet, so that adjacent wire portions form kinks alternately projecting in opposite directions so that every second kink projects toward the copy sheet and forms a small engaging portion preventing scorching of the copy sheet when the copy sheet curls due to the heat.

6 Claims, 1 Drawing Figure 26c CUPY-SHEEI BACKGROUND OF THE INVENTION The present invention relates to a fixing device for electrophotographic copiers, in which a powder image on a copy sheet is fixed by the application of heat while passing sources of heat.

It is known to provide apparatus of this type with means which are to prevent a scorching of a copy sheet, maintaining the copy at a safe distance from the heaters.

In order to prevent contact between the copy sheet and the heaters, which would result in scorching, it is known to provide spacing wires located between the heaters and the copy sheet passing the heaters. In accordance with the prior art, the spacing wires are straight, or slightly curved.

The arrangement of the prior art has the disadvantage that the copy sheets which are freely transported through the drying and fixing device, are either slightly bent and curved, or curl when heated by the heaters. Due to such curvature of the sheet, a long portion of the copy sheet may be in contact with the hot spacing wires, and consequently scorched.

SUMMARY OF THE INVENTION It is one object of the invention to reduce the time of contact between a copy sheet and a spacing wire during passage of said copy sheet through a fixing device.

Another object of the invention is to reduce the area of contact between the copy sheet and the spacing wire.

Another object of the invention is to provide a spacing means with a plurality of engaging portions projecting toward the copy sheet, and permit contact between the spacing means and the copy sheet only on small areas of the copy sheet.

With these objects in view, the present invention provides spacing means, preferably at least one spacing wire which has engaging portions spaced from each other and adapted to be in contact with the copy sheet. Preferably, alternate portions of the spacing wire are bent in opposite directions so that kinks are formed in the wire, every second kink projecting toward the copy sheet. The kinks are preferably spaced from each other distances which are between one fifth and one tenth of the length of the copy sheet. The distances are preferably equal.

The periods and amplitudes of the kinks or bent wire portions are preferably selected so that the copy sheet does not follow the general curvature of the wire, but only is in contact'with the projecting engaging portions for a short distance so that only a small portion of the copy sheet is heated by the" respective engaging portions of the spacing wire, and scorching of the copy sheet is reliably prevented.

The novel features which are considered as characteristic for the invention are set forth in particular in the in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE of the drawing is a longitudinal sectional view illustrating an embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT A housing 1 is provided with a guide for inserting a heating device 3 in accordance with the invention. A carrier 4 in the device 3 supports the electric heating coil 5. The device 3 carries in addition to the main heating means 4, 5, also an additional heating means 23 which is covered by a guide plate 24. The additional heating means 23 is provided with reflectors 25, and the main heating means 4, 5 is provided with reflectors 26, 27. A gap is formed between the guide plate 24 and the main heating means 4, 5, and a copy sheet 30, carrying a powder image, is inserted in the direction of the arrow into the device 3 along a path determined by the guide plate 24 which is preferably slightly curved and concave toward the heating means 4, 5. Between the heating means 4, 5 and the guide plate 24, a spacing means is provided which is shown to be a spacing wire 28 whose ends are secured to the casing of the device 3. Two spacing wires 28 may be provided for engagement with the two marginal portions of a copy sheet 30 on guide plate 24 so that there can be no contact be tween the spacing wires 28 and the powder image on the copy sheet.

Due to the provision of the spacing wire, or spacing wires 28, the copy sheet on guide plate 24 cannot engage the heating means 4, 5 when curling due to the influence of the heat radiated by the heating means 4, 5 and 23.

As clearly shown in the drawing, each spacing wire 28 extends along the path of movement of the copy sheet, and has a plurality of wire portions 280 and 28d alternately bent in opposite directions toward and away from the path of the copy sheet, so that adjacent wire portions form kinks 28a and 28b. Every second kink 28a projects toward the copy sheet and its guide plate 24, and is engaged by the copy sheet when the same curls up or is curved for any other reason.

The amplitude of the bent wire portions 28c, 28d, and the spacing between the kinks is selected so that the used copy sheet cannot assume the same curvature as the spacing wire 28.

It is advantageous to space the effective kinks 28a apart by distances which are between one fifth and one tenth of the length of the copy sheet 30, corresponding substantially to the length of the guide plate 24. An electrostatically charged drum 29 supplies copy sheets 30 into an inlet 3a in the housing means of the heating device 3, and the leading end of the copy sheet is gripped by a pair of transporting rollers 31, 32 which move the copy sheet out of the outlet 30. The transporting rollers 31, 32 are automatically coupled to drive means in the housing 1 when the heating device 3 is inserted into housing means 1, 2.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of electrophotographic copying apparatus differing from the type described above.

While the invention has been illustrated and described as embodied in an electrophotographic fixing device provided with a kinked spacing wire between the copy sheet and the heating means, it is not intended to be limited to the details shown, sin'ce various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

We claim:'

1. A device for fixing powder images on copy sheets in electrophotographic copying apparatus, comprising means for moving poweder image carrying copy sheets lengthwise in a predetermined direction along an elongated path; heating means adjacent to a portion of said path and defining an elongated heating zone, as considered in said direction, said heating means comprising a plurality of heating elements; and spacing means disposed between said heating means and said portion of said path for maintaining a copy sheet in said portion of said path out of contact with said heating elements while the copy sheet moves past said heating zone and exhibits a tendency to curl as a result of heating, including at least one elongated wire disposed in and extending substantially along the full length of said heating zone between said heating means and said portion of said path, said wire having a plurality of successive por- 4 tions alternately bent in opposite directions toward and away from said path so that the neighboring portions of said wire form a first group of kinks nearer to said heating means and a second group of kinks alternating with the kinks of said first group and nearer to said portion of said path whereby the kinks of said second group maintain a copy sheet in said portion of said path ata distance from said heating means which suffices to prevent scorching of the sheet.

2. A device as defined in claim 1 for fixing powder I adjacent to a marginal portion of a copy sheet in said portion of said path, the distance between successive kinks of said second group of kinks in each of said wires being between one-fifth and one-tenth of said predetermined length.

3. A device as defined in claim 2, wherein said guide plate is elongated, as considered in said predetermined direction, and said means for moving copy sheets comprises a pair of transporting rollers located at one end of said guide plate.

4. A device as defined in claim 2, wherein said guide plate has a slightly curved concave side facing said portion of said path.

5. A device as defined in claim 1, wherein the general outline of said wire isslightly curved and convex toward said portion of said path.

6. A device as defined in claim I, wherein the neighboring kinks of said second group are spaced apart by identical distances. 

1. A device for fixing powder images on copy sheets in electrophotographic copying apparatus, comprising means for moving poweder image carrying copy sheets lengthwise in a predetermined direction along an elongated path; heating means adjacent to a portion of said path and defining an elongated heating zone, as considered in said direction, said heating means comprising a plurality of heating elements; and spacing means disposed between said heating means and said portion of said path for maintaining a copy sheet in said portion of said path out of contact with said heating elements while the copy sheet moves past said heating zone and exhibits a tendency to curl as a result of heating, including at least one elongated wire disposed in and extending substantially along the full length of said heating zone between said heating means and said portion of said path, said wire having a plurality of successive portions alternately bent in opposite directions toward and away from said path so that the neighboring portions of said wire form a first group of kinks nearer to said heating means and a second group of kinks alternating with the kinks of said first group and nearer to said portion of said path whereby the kinks of said second group maintain a copy sheet in said portion of said path at a distance from said heating means which suffices to prevent scorching of the sheet.
 2. A device as defined in claim 1 for fixing powder images on copy sheets having two parallel marginal portions and a predetermined length, wherein said heating zone is adjacent to one side of said path and further comprising a fixed guide plate adjacent to the other side of said path opposite said heating zone, said spacing means comprising two elongated wires each adjacent to a marginal portion of a copy sheet in said portion of said path, the distance between successive kinks of said second group of kinks in each of said wires being between one-fifth and one-tenth of said predetermined length.
 3. A device as defined in claim 2, wherein said guide plate is elongated, as considered in said predetermined direction, and said means for moving copy sheets comprises a pair of transporting rollers located at one end of said guide plate.
 4. A device as defined in claim 2, wherein said guide plate has a slightly curved concave side facing said portion of said path.
 5. A device as defined in claim 1, wherein the general outline of said wire is slightly curved and convex toward said portion of said path.
 6. A device as defined in claim 1, wherein the neighboring kinks of said second group are spaced apart by identical distances. 